Cu-mn-zn resistance alloy



United States Patent Westinghouse Electric Corporation, East Pittsburgh,

Pa., a corporation of Pennsylvania No Drawing. Application January 21, 1954, Serial No. 405,517

6 Claims. (Cl. 75--157.5)

This invention relates. to a novel copper-manganesezinc alloy suitable for use in high electrical resistance castings.

The alloys heretofore finding extensive use in casting high electrical resistance elements have been generally of two types: one has been a copper base alloy containing manganese, zinc, aluminum and substantially iron; while the other type has been a copper base alloy containing substantially 45% nickel. The copper base alloy containing iron has the disadvantage in that it is difiicnlt to maintain a proper chemical composition with respect to the iron content. iron in the amounts required for desired electrical resistance characteristics, is not readily soluble in copper, and thus it is difficult to maintain the iron content within the necessary range. Further, there is a tendency for the iron to form extremely hard particles comprising an iron-manganese complex, which cannot be machined except by grinding.

The copper base alloy containing nickel presents no problem in maintaining a proper chemical composition, however, trouble is encountered in consistently manufacturing sound castings. The nickel content of this alloy makes the metal susceptible to gas absorption during melting which subsequently causes gas porosity in the casting during solidification. Porosity in the castings causes uncontrollable variation of electrical characteristics of the castings making them unsatisfactory for electrical resistance elements. Furthermore, because of the high nickel content therein, this alloy is not readily available during periods of limited supply of nickel.

An object of this invention is to provide an alloy comprising as its essential ingredients a critical ratio of copper, manganese, and zinc, which is suitable for use in casting high electrical resistance elements;

Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.

For a more complete understanding of the nature and objects of the invention, reference should be had to the following detailed description.

I have discovered an alloy having a critical ratio of copper, manganese and zinc, which alloy possesses mechanical and electrical propertiesparticularly suited for use in casting electrical resistance elements. The alloy comprises as its essential ingredients from 10 to 12.5% by weight of manganese, from 9 to 13% by weight of zinc, and the balance being copper. If desirable, from 0.25 to 1.25% by weight aluminum may be added to the alloy, whereby its castability can be improved without affecting its electrical properties. There may also be present in the alloy, without adversely aifecting its electrical and mechanical properties, a maximum of 1.25% by weight of iron, 0.5% by weight lead and 0.5% by Weight tin.

Table I cordance with this invention.

Alloy Copper Manganese Zinc Aluminum The results of tensile tests and electrical conductivity determinations on sand cast test bars, having chemical compositions within the range set forth above, shows that the following minimum mechanical properties can be expected.

Tensile strength, p. s. i 33,000

Yield strength, p. s. i 18,000 Elongation in 2", percent 12 The average electrical conductivity of these alloys as determined on the test bars is 3.9% of the conductivity of copper. Analyses have shown, with 99% certainty, that the electrical conductivity of separately cast test bars of the alloys of this invention will fall within the range of 3.5% to 4.3%, 100% conductivity being based on copper having a resistance of 0.15328 ohm permeter gram at 20 C. (68 F.). 7

Yield strength as used herein is defined as the stress producing 0.5% extension of the test bar in a 2" gauge length.

The electrical resistance elements cast from the alloys of this invention are easily cast and machined and are consistently uniform in mechanical and electrical properties.

Since certain obvious changes may be made in the above procedure and dilierent embodiments of the invention could be made without departing from the spirit and scope thereof, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention: 1

1. A cast electrical resistance member composed of an alloy comprising as its essential ingredients from 10 to 12.5% by weight manganese, from 9 to 13% by weight zinc and the balance being copper, the cast members of the alloy having from 3.5% to 4.3% of the electrical conductivity of copper.

2. The alloy of claim 1 in which there is present from 0.25 to 1.25% by weight aluminum.

3. The alloy of claim 1 in which there is present not more than 1.25 by weight iron.

4. The alloy of claim 2 in which there is present not more than 1.25% by weight iron.

5. A cast electrical resistance member composed of an alloy comprising as its essential ingredients from 10 to 12.5% by weight manganese, from 9 to 13% by weight zinc, from 0% to 1.25% by weight aluminum, from 0% to 1.25% by weight iron and the balance being copper, the cast members of the alloy having from 3.5% to 4.3% of the electrical conductivity of copper.

6. The alloy of claim 5 in which there is present from O to 0.5 by weight lead and from '0 to 0.5% by weight tin.

References Cited in the file of this patent UNITED STATES PATENTS 2,479,596 Anderson et a1. Aug, 23, 1949 FOREIGN PATENTS 133,362 Great Britain June 20, 1918 OTHER REFERENCES Engineering Alloys, 1936 ed., page 177. Edited by Woldman and Dornblatt. 

1. A CAST ELECTRICAL RESISTANCE MEMBER COMPOSED OF AN ALLOY COMPRISING AS ITS ESSENTIAL INGREDIENTS FROM 10 TO 12.5% BY WEIGHT MANGANESE, FROM 9 TO 13% BY WEIGHT ZINC AND THE BALANCE BEING COPPER, THE CAST MEMBERS OF THE ALLOY HAVING FROM 3.5% TO 4.3% OF THE ELECTRICAL CONDUCTIVITY OF COPPER. 